( function () {
/**
 * A shadow THREE.Mesh that follows a shadow-casting THREE.Mesh in the scene, but is confined to a single plane.
 */

const _shadowMatrix = new THREE.Matrix4();

class ShadowMesh extends THREE.Mesh {
  constructor(mesh) {
    const shadowMaterial = new THREE.MeshBasicMaterial({
      color: 0x000000,
      transparent: true,
      opacity: 0.6,
      depthWrite: false
    });
    super(mesh.geometry, shadowMaterial);
    this.meshMatrix = mesh.matrixWorld;
    this.frustumCulled = false;
    this.matrixAutoUpdate = false;
  }

  update(plane, lightPosition4D) {
    // based on https://www.opengl.org/archives/resources/features/StencilTalk/tsld021.htm
    const dot = plane.normal.x * lightPosition4D.x + plane.normal.y * lightPosition4D.y + plane.normal.z * lightPosition4D.z + -plane.constant * lightPosition4D.w;
    const sme = _shadowMatrix.elements;
    sme[0] = dot - lightPosition4D.x * plane.normal.x;
    sme[4] = -lightPosition4D.x * plane.normal.y;
    sme[8] = -lightPosition4D.x * plane.normal.z;
    sme[12] = -lightPosition4D.x * -plane.constant;
    sme[1] = -lightPosition4D.y * plane.normal.x;
    sme[5] = dot - lightPosition4D.y * plane.normal.y;
    sme[9] = -lightPosition4D.y * plane.normal.z;
    sme[13] = -lightPosition4D.y * -plane.constant;
    sme[2] = -lightPosition4D.z * plane.normal.x;
    sme[6] = -lightPosition4D.z * plane.normal.y;
    sme[10] = dot - lightPosition4D.z * plane.normal.z;
    sme[14] = -lightPosition4D.z * -plane.constant;
    sme[3] = -lightPosition4D.w * plane.normal.x;
    sme[7] = -lightPosition4D.w * plane.normal.y;
    sme[11] = -lightPosition4D.w * plane.normal.z;
    sme[15] = dot - lightPosition4D.w * -plane.constant;
    this.matrix.multiplyMatrices(_shadowMatrix, this.meshMatrix);
  }

}

ShadowMesh.prototype.isShadowMesh = true;

THREE.ShadowMesh = ShadowMesh;
} )();
